From your description, I think something is wrong - driveshaft, wheel bearing, damper, etc. and it should be fixed before you do anything else.
A taller tire has exactly the same effect on speed as a ratio change: new ÷ old = change.
Replacing a 27" tire with a 28" tire increases speed by 28 ÷ 27 = 1.037.
50 mph become 51.85 mph.
You can't get 10 mph out of a tire change.
